The present invention relates to a display device and to a method of manufacture thereof, for example, to an active matrix type liquid crystal display device, an organic EL display device or the like.
In the active matrix type display device, on a surface of a substrate thereof, regions which are surrounded by gate signal lines (scanning signal lines), which extend in the x direction and are arranged in parallel in the y direction, and drain signal lines (video signal lines), which extend in the y direction and are arranged in parallel in the x direction, are defined as pixel regions, and an array of these pixel regions constitutes a display part.
Each pixel region is provided with a switching element, which is driven by a scanning signal received from a one-side gate signal line of a pair of gate signal lines which surround the pixel region, and an electrode, to which a video signal is supplied from the one-side drain signal line of a pair of drain signal lines which surround the pixel region, by way of the switching element.
The electrode is configured so that a voltage difference corresponding to the video signal is generated between the electrode and another electrode, which is arranged with liquid crystal sandwiched therebetween in the case of a liquid crystal display device.
In the case of an organic EL display device, although there are several methods, as one example, the electrode is constituted of an electrode of a capacitive element which receives the video signal. Here, the organic EL display device includes a circuit which generates an electric current which corresponds to the video signal between one electrode and another electrode, which electrodes are arranged between organic light emitting layers, in response to a video signal received by the capacitive element.
Although a display device having such a constitution is configured such that respective pixels of the display part are driven by sequentially scanning the pixel groups (lines) which use the gate signal lines in common, the display device includes a capacitive element which can store the video signal supplied to the pixel group until the same pixel group is the driven next time.
The above-mentioned switching element (for example, a thin film transistor) and capacitive element are respectively constituted of a stacked body having a given pattern which is formed of a semiconductor layer, an insulation layer, a metal layer and the like. Here, a gate insulation film of the switching element and a dielectric film of the capacitive element are usually formed of a common insulation film, which technique is employed for reducing the complexity of the manufacturing process.
However, in the above-mentioned constitution, since the characteristics of the thin film transistor are predetermined, the film thickness of the gate insulation film of the thin film transistor is preliminarily regulated, and, hence, there arises a drawback in that the film thickness of the dielectric film of the capacitive element is also predetermined. That is, with respect to the capacitive element formed in the inside of the pixel region, even when an attempt is made to increase a relatively large capacitance, since the film thickness of the dielectric film is predetermined, the area of the dielectric film must be inevitably increased, resulting in a lowering of a so-called numerical aperture.
Accordingly, a technique has been proposed in the form of a newly added step in which the dielectric film of the capacitive element is made thinner than the gate insulation film of the thin film transistor. In this technique, the gate insulation film, which is formed in a region where the capacitive element is formed, is removed by selective etching using a mask, thus forming a thermal oxide film after removing the mask.
Such a technique is disclosed, for example, in Japanese Unexamined Patent Publication Hei6(1994)-175154.